The present disclosure relates generally to toners and toner processes, and more specifically, to toner compositions with improved melt flow.
In electrophotography, an image is produced by forming an electrostatic latent image on a surface of a photoreceptor having a drum or belt shape, or the like, developing the electrostatic latent image with a toner so as to obtain a toner image, electrostatically transferring the toner image onto a recording media such as paper directly or via an intermediate transfer member, and fusing the toner onto a surface of the recording paper by heating, or the like.
A number of aspects of the overall print quality are affected by the rheology, or viscoelasticity, of the toners used to develop the print. The aspects of the overall print quality affected include overall gloss level of the image, the differential gloss of the image, the fix level of the image (for example as measured by either crease or rub testing), color-to-color fix level differences, and image quality defects associated with offset of the image, either to the fusing roll during the fusing process (hot offset) or to other surfaces after the print has exited the machine (vinyl or document offset). In addition, toner rheology also affects toner fuser roll life, for example, the rate at which toner builds up on the toner fuser roll of an image forming device using the toner to develop images.
Toner may be made by an emulsion aggregation process. Methods of preparing an emulsion aggregation (EA) type toner are known and toners may be formed by aggregating a colorant with a latex polymer formed by batch or semi-continuous emulsion polymerization. For example, U.S. Pat. No. 5,853,943, the disclosure of which is hereby incorporated by reference in its entirety, is directed to a semi-continuous emulsion polymerization process for preparing a latex by first forming a seed polymer. In particular, the '943 patent describes a process including: (i) conducting a pre-reaction monomer emulsification which includes emulsification of the polymerization reagents of monomers, chain transfer agent, a disulfonate surfactant or surfactants, and optionally an initiator, wherein the emulsification is accomplished at a low temperature of, for example, from about 5° C. to about 40° C.; (ii) preparing a seed particle latex by aqueous emulsion polymerization of a mixture including (a) part of the monomer emulsion, from about 0.5 to about 50 percent by weight, or from about 3 to about 25 percent by weight, of the monomer emulsion prepared in (i), and (b) a free radical initiator, from about 0.5 to about 100 percent by weight, or from about 3 to about 100 percent by weight, of the total initiator used to prepare the latex polymer at a temperature of from about 35° C. to about 125° C., wherein the reaction of the free radical initiator and monomer produces the seed latex comprised of latex resin wherein the particles are stabilized by surfactants; (iii) heating and feed adding to the formed seed particles the remaining monomer emulsion, from about 50 to about 99.5 percent by weight, or from about 75 to about 97 percent by weight, of the monomer emulsion prepared in (ii), and optionally a free radical initiator, from about 0 to about 99.5 percent by weight, or from about 0 to about 97 percent by weight, of the total initiator used to prepare the latex polymer at a temperature from about 35° C. to about 125° C.; and (iv) retaining the above contents in the reactor at a temperature of from about 35° C. to about 125° C. for an effective time period to form the latex polymer, for example from about 0.5 to about 8 hours, or from about 1.5 to about 6 hours, followed by cooling. Other examples of emulsion/aggregation/coalescing processes for the preparation of toners are illustrated in U.S. Pat. Nos. 5,290,654, 5,278,020, 5,308,734, 5,370,963, 5,344,738, 5,403,693, 5,418,108, 5,364,729, and 5,346,797, the disclosures of each of which are hereby incorporated by reference in their entirety. Other processes are disclosed in U.S. Pat. Nos. 5,348,832, 5,405,728, 5,366,841, 5,496,676, 5,527,658, 5,585,215, 5,650,255, 5,650,256 and 5,501,935, the disclosures of each of which are hereby incorporated by reference in their entirety.
In view of the recent demand for high image quality, toner with improved fusing, for example improved melt is desired. Melt flow index is an accurate reflection of the rheology, or viscoelasticity, of the toners used to develop a print. Hence, an improved melt flow index of a toner is an indication of an improved print quality.
In the developing and transferring properties of a toner, the molecular weight of the toner exhibits large influence on performance, reliability, and melt flow. Toners made by the above methods may have a molecular weight below about 50 kpse. Toners with a molecular weight below 50 kpse may be used in single component development systems. The low molecular weight toners flow well through these development systems. Unfortunately, these low molecular weight toners tend to lose their charge and form in the toner housing such that they consequentially break or are easily crushed. Hence, these low molecular weight toners are not as robust as higher molecular weight toners. In contrast, higher molecular weight toners typically do not flow well resulting in poor image quality.
Hence, it would be advantageous to provide a toner composition with high molecular weight latex that has an improved melt flow index.